An internal combustion engine is provided with such affiliated instruments or systems as an ignition system, a fuel injection system and an exhaust valve to control an exhaust timing which have such a controlled variable as an operation period or an operation amount in accordance with a phase at which a drive signal is given and/or a signal width of the drive signal.
For instance, the ignition system comprises an ignition circuit to generate an igniting high voltage when the ignition signal or drive signal is applied thereto and ignition position control means to control an ignition position which corresponds to the period at which an ignition operation is made and which is indicated by a rotary angle position of a crank shaft. The ignition position control means serves to determine the ignition position relative to the revolution of the engine, the opening degree of the throttle valve and so on and to supply an ignition signal to the ignition circuit at the determined ignition position.
The fuel injection system comprises an injector such as an electromagnet type fuel injecting valve including an electromagnet and a valve driven by the electromagnet and serving to open the valve while the drive current is received to inject the fuel, injection instruction means to make an arithmetical operation of a fuel injection time (a period during which the fuel is injected) and the ignition start position (a time at which the fuel injection starts and which is indicated by the rotary angle position of the crank shaft) relative to the revolution of the engine and the opening degree of the throttle valve to generate an injection instruction signal of rectangular wave having a time width corresponding to the thus obtained fuel injection time at the thus obtained injection start time and an injector drive circuit to flow the drive current through the injector while the injection instruction signal is given. Since a pressure of the fuel applied to the injector is kept constant, the amount of fuel (the operation amount) injected from the injector is determined on the signal width of the injection instruction signal.
The exhaust valve is provided in an exhaust port of a two cycle internal combustion engine and has an opening degree (an operation amount) controlled in accordance with the revolution of the engine and the opening degree of the throttle valve.
A control system having a microcomputer used has been employed for controlling these affiliated instruments of the internal combustion engine.
A prior control system for the internal combustion engine such as one for the ignition system, for example is adapted to detect a revolution of the engine from the distance (period) at which a picking up coil generates a plurality of signals at a predetermined rotary angle position of the internal combustion engine and to make an arithmetical operation of the ignition position on the next rotation of the engine (the rotary angle position of the crank shaft when the engine is ignited) by using the detected revolution in a job done every constant time distance by a main routine of a program practiced by the microcomputer.
As a result, although the picking up coil detects the revolution of the engine whenever it generates the signal (every rotation of the crank shaft), the ignition operation is made in accordance with an ignition position data determined on the revolution of the engine detected before the present revolution of the engine is detected. This disadvantageously causes the ignition position to be delayed relative to a change in the revolution of the engine.
In the condition that the revolution of the engine is kept stable, such a delay in the control of the ignition position may be allowed, but when the engine is driven at a relatively lower speed or on a rapid acceleration or deceleration so that the change in the revolution of the engine is relatively larger, the delay in the control will adversely affect the operation of the engine so that the rotation of the engine gets unstable or a performance in the acceleration of the engine will decrease.
As the internal combustion engine is specifically of two cycle type, for example, irregular combustion occurs at the low speed and it provides a large variation in the rotation of the engine due to deviation of the ignition position from the appropriate one. Thus, it is desirable to precisely control the ignition position of the engine relative to the instantaneous revolution of the engine ever one cycle thereof when it is driven at the low speed.
In order to solve the aforementioned problems, it will be considered to make an arithmetical operation of the ignition position using a map for the arithmetic operation of the ignition position immediately after the revolution is detected in an interruption routine practiced when the picking up coil generates a signal.
However, if a three-dimensional map is used as the map for the arithmetical operation of the ignition position, then it will take much time to make the arithmetical operation of the ignition position relative to the control conditions such as the revolution, the opening degree of the throttle valve and so on. Thus, with the ignition position determined in the interruption routine practiced when the revolution of the engine is detected, the arithmetical operation of the ignition position will be not in time and therefor the engine will fail to make the ignition operation.
Although the disadvantages of the control system for the internal combustion engine have been explained about the ignition system therefor as the control object, the same problems will occurs with other affiliated instruments as the control objects such as the fuel injection system in which the injection start period and the injection time should be controlled, if they are controlled so as to make the arithmetical operation of an objective value of the controlled variable in the same manner.